Effects Of Wheat Phenolic Acids On The Growth And Development And Detoxification Enzyme Activities Of Sitobion Avenae

The English grain aphid,Sitobion avenae（Fabricius）,is an important pest in various wheat producing areas in China.It can cause severe losses in wheat production.Planting aphid resistant varieties of wheat is an economical and efficient way to control S.avenae.Phenolic acids are secondary metabolites in wheat,which play an important role in wheat resistance to aphids.In this study,11 phenolic acid compounds in wheat were tested for the insecticidal activity against S.avenae,and three of the most active compounds were selected for further experiments.In addition,the effects of these compounds at sublethal concentrations on the growth,development and reproduction of S.avenae were also tested.Finally,in order to explore the mechanism of insecticidal activity,detoxification enzyme activity and related gene expression changes of S.avenae after feeding on diets with these three phenolic acids were explored.The results are as follows:1.Investigation of the insecticidal activity of 11 phenolic acid compounds against second instar S.avenae was conducted.The results showed that after 96 hours of feeding,the highest insecticidal activities against second-instar aphids were found for protocatechuic acid,2,5-dihydroxybenzoic acid and syringic acid,with corresponding LC₅₀values of537.82 mg/L,849.10 mg/L and 889.88 mg/L,respectively.Their insecticidal activity was comparable to that of the positive control rotenone(LC₅₀was 668.60 mg/L).Therefore,these three phenolic acid compounds were selected for further experiments.Three phenolic acids with different concentrations were used to spray wheat outdoors.The results showed that 1000 mg/L concentration of the three phenolic acids could significantly reduce the number of S.avenae compared to the control group after 14 days of treatment,and2,5-dihydroxybenzoic acid significantly reduced the number of aphids compared to the control group after 7,14,and 21 days of treatment.These results indicate that2,5-dihydroxybenzoic acid may have potential application value.2.The artificial diet with sublethal concentrations(LC₁₀and LC₃₀)of three phenolic acids was used to feed the second instar S.avenae,and their effects on the life history of S.avenae were investigated.Results showed that all three phenolic acids significantly prolonged the population doubling time.They also significantly decreased the net reproductive rate,intrinsic rate of increase,and finite rate of increase of S.avenae populations,with greater reductions observed at highter concentrations.2,5-dihydroxybenzoic acid and syringic acid could significantly prolonged the total developmental period of S.avenae at both sublethal concentrations.The sublethal concentration of three phenolic acids significantly reduced the fecundity and adult weight and shortened the adult period of S.avenae.3.The artificial diet with three phenolic acids at different concentrations(LC₃₀and LC₆₀)was used to feed the second instar S.avenae for 96 hours,and their effects on the activities of three detoxification enzymes in S.avenae were determined.The results showed that the glutathione S-transferase（GST）activity in S.avenae significantly increased than that of the control group after 96 hours of feeding with LC₃₀concentration of syringic acid and LC₆₀concentration of 2,5-dihydroxybenzoic acid,while the induction effect of GST activity by protocatechuic acid at both concentrations was not significant.Compared with the control group,the treatment with LC₆₀concentration of syringic acid significantly inhibited the carboxylesterase（CarE）activity in S.avenae,but other phenolic acids treatments did not show significant differences in CarE activity.Both concentrations of protocatechuic acid and syringic acid treatments significantly inhibited the activity of acetylcholinesterase（AchE）compared to the control group,while 2,5-dihydroxybenzoic acid significantly activated the AchE activity compared to the control group.4.The artificial diet with three phenolic acids at different concentrations(LC₃₀and LC₆₀)were used to feed the second instar S.avenae for 96 hours,and their effects on the expression levels of three detoxifying enzyme genes in S.avenae were determined.The results showed that,the expression of SaGSTT1 gene was significantly up-regulated by the three phenolic acids compared with the control group.It was speculated that SaGSTT1 gene may be the key gene in regulating the detoxification metabolism of S.avenae to phenolic acid.Compared with the control group,only LC₆₀concentration of protocatechuic acid significantly up-regulated the expression of SaCarE6 gene,while other phenolic acids treatments did not show significant differences.The expression of SaAchE1 gene was significantly down-regulated after feeding the S.avenae with LC₃₀and LC₆₀concentrations of Syringic acid,LC₃₀concentration of protocatechuic acid and 2,5-dihydroxybenzoic acid compared with the control group,but the expression of SaAchE1 gene was significantly up-regulated after feeding treatment with LC₆₀concentration of protocatechuic acid and2,5-dihydroxybenzoic acid compared with the control group.In summary,the insecticidal activity of 11 phenolic acids against S.avenae was measured in this study,and three compounds with the highest insecticidal activity were selected for further experiments.It was found that spraying wheat with three phenolic acids over a period of time could reduce the population of S.avenae.The growth,development and reproduction of S.avenae were significantly inhibited after feeding the artificial diet containing three phenolic acids,and the detoxification enzyme activities and related gene expression of S.avenae were also changed.These results indicate that different phenolic acids can cause different physiological and biochemical reactions in S.avenae,and the specific regulatory mechanism needs further study.This study provides a theoretical basis for using phenolic acids in wheat to control S.avenae,and also a reference for further exploring the detoxification metabolism process of S.avenae for phenolic acids in wheat.